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<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_asio.reference.io_service"></a><a class="link" href="io_service.html" title="io_service">io_service</a>
</h3></div></div></div>
<p>
        <a class="indexterm" name="boost_asio.indexterm.io_service"></a> 
Typedef for backwards compatibility.
      </p>
<pre class="programlisting">typedef io_context io_service;
</pre>
<h5>
<a name="boost_asio.reference.io_service.h0"></a>
        <span class="phrase"><a name="boost_asio.reference.io_service.types"></a></span><a class="link" href="io_service.html#boost_asio.reference.io_service.types">Types</a>
      </h5>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                <p>
                  Name
                </p>
              </th>
<th>
                <p>
                  Description
                </p>
              </th>
</tr></thead>
<tbody>
<tr>
<td>
                <p>
                  <a class="link" href="io_context__basic_executor_type.html" title="io_context::basic_executor_type"><span class="bold"><strong>basic_executor_type</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Executor implementation type used to submit functions to an io_context.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context__service.html" title="io_context::service"><span class="bold"><strong>service</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Base class for all io_context services.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context__strand.html" title="io_context::strand"><span class="bold"><strong>strand</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Provides serialised handler execution.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context__work.html" title="io_context::work"><span class="bold"><strong>work</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  (Deprecated: Use executor_work_guard.) Class to inform the io_context
                  when it has work to do.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/count_type.html" title="io_context::count_type"><span class="bold"><strong>count_type</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  The type used to count the number of handlers executed by the context.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/executor_type.html" title="io_context::executor_type"><span class="bold"><strong>executor_type</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Executor used to submit functions to an io_context.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/fork_event.html" title="io_context::fork_event"><span class="bold"><strong>fork_event</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Fork-related event notifications.
                </p>
              </td>
</tr>
</tbody>
</table></div>
<h5>
<a name="boost_asio.reference.io_service.h1"></a>
        <span class="phrase"><a name="boost_asio.reference.io_service.member_functions"></a></span><a class="link" href="io_service.html#boost_asio.reference.io_service.member_functions">Member
        Functions</a>
      </h5>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                <p>
                  Name
                </p>
              </th>
<th>
                <p>
                  Description
                </p>
              </th>
</tr></thead>
<tbody>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/dispatch.html" title="io_context::dispatch"><span class="bold"><strong>dispatch</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  (Deprecated: Use boost::asio::dispatch().) Request the io_context
                  to invoke the given handler.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/get_executor.html" title="io_context::get_executor"><span class="bold"><strong>get_executor</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Obtains the executor associated with the io_context.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/io_context.html" title="io_context::io_context"><span class="bold"><strong>io_context</strong></span></a> <span class="silver">[constructor]</span>
                </p>
              </td>
<td>
                <p>
                  Constructor.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/notify_fork.html" title="io_context::notify_fork"><span class="bold"><strong>notify_fork</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Notify the execution_context of a fork-related event.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/poll.html" title="io_context::poll"><span class="bold"><strong>poll</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Run the io_context object's event processing loop to execute ready
                  handlers. <br> <span class="silver"> —</span><br> (Deprecated: Use non-error_code overload.)
                  Run the io_context object's event processing loop to execute ready
                  handlers.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/poll_one.html" title="io_context::poll_one"><span class="bold"><strong>poll_one</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Run the io_context object's event processing loop to execute one
                  ready handler. <br> <span class="silver"> —</span><br> (Deprecated: Use non-error_code overload.)
                  Run the io_context object's event processing loop to execute one
                  ready handler.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/post.html" title="io_context::post"><span class="bold"><strong>post</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  (Deprecated: Use boost::asio::post().) Request the io_context to
                  invoke the given handler and return immediately.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/reset.html" title="io_context::reset"><span class="bold"><strong>reset</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  (Deprecated: Use restart().) Reset the io_context in preparation
                  for a subsequent run() invocation.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/restart.html" title="io_context::restart"><span class="bold"><strong>restart</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Restart the io_context in preparation for a subsequent run() invocation.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/run.html" title="io_context::run"><span class="bold"><strong>run</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Run the io_context object's event processing loop. <br> <span class="silver"> —</span><br>
                  (Deprecated: Use non-error_code overload.) Run the io_context object's
                  event processing loop.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/run_for.html" title="io_context::run_for"><span class="bold"><strong>run_for</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Run the io_context object's event processing loop for a specified
                  duration.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/run_one.html" title="io_context::run_one"><span class="bold"><strong>run_one</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Run the io_context object's event processing loop to execute at
                  most one handler. <br> <span class="silver"> —</span><br> (Deprecated: Use non-error_code
                  overload.) Run the io_context object's event processing loop to
                  execute at most one handler.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/run_one_for.html" title="io_context::run_one_for"><span class="bold"><strong>run_one_for</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Run the io_context object's event processing loop for a specified
                  duration to execute at most one handler.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/run_one_until.html" title="io_context::run_one_until"><span class="bold"><strong>run_one_until</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Run the io_context object's event processing loop until a specified
                  time to execute at most one handler.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/run_until.html" title="io_context::run_until"><span class="bold"><strong>run_until</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Run the io_context object's event processing loop until a specified
                  time.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/stop.html" title="io_context::stop"><span class="bold"><strong>stop</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Stop the io_context object's event processing loop.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/stopped.html" title="io_context::stopped"><span class="bold"><strong>stopped</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Determine whether the io_context object has been stopped.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/wrap.html" title="io_context::wrap"><span class="bold"><strong>wrap</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  (Deprecated: Use boost::asio::bind_executor().) Create a new handler
                  that automatically dispatches the wrapped handler on the io_context.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/_io_context.html" title="io_context::~io_context"><span class="bold"><strong>~io_context</strong></span></a> <span class="silver">[destructor]</span>
                </p>
              </td>
<td>
                <p>
                  Destructor.
                </p>
              </td>
</tr>
</tbody>
</table></div>
<h5>
<a name="boost_asio.reference.io_service.h2"></a>
        <span class="phrase"><a name="boost_asio.reference.io_service.protected_member_functions"></a></span><a class="link" href="io_service.html#boost_asio.reference.io_service.protected_member_functions">Protected
        Member Functions</a>
      </h5>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                <p>
                  Name
                </p>
              </th>
<th>
                <p>
                  Description
                </p>
              </th>
</tr></thead>
<tbody>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/destroy.html" title="io_context::destroy"><span class="bold"><strong>destroy</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Destroys all services in the context.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/shutdown.html" title="io_context::shutdown"><span class="bold"><strong>shutdown</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Shuts down all services in the context.
                </p>
              </td>
</tr>
</tbody>
</table></div>
<h5>
<a name="boost_asio.reference.io_service.h3"></a>
        <span class="phrase"><a name="boost_asio.reference.io_service.friends"></a></span><a class="link" href="io_service.html#boost_asio.reference.io_service.friends">Friends</a>
      </h5>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                <p>
                  Name
                </p>
              </th>
<th>
                <p>
                  Description
                </p>
              </th>
</tr></thead>
<tbody>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/add_service.html" title="io_context::add_service"><span class="bold"><strong>add_service</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  (Deprecated: Use make_service().) Add a service object to the execution_context.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/has_service.html" title="io_context::has_service"><span class="bold"><strong>has_service</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Determine if an execution_context contains a specified service
                  type.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/make_service.html" title="io_context::make_service"><span class="bold"><strong>make_service</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Creates a service object and adds it to the execution_context.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="io_context/use_service.html" title="io_context::use_service"><span class="bold"><strong>use_service</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  <br> <span class="silver"> —</span><br> Obtain the service object corresponding to the given
                  type.
                </p>
              </td>
</tr>
</tbody>
</table></div>
<p>
        The <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a>
        class provides the core I/O functionality for users of the asynchronous I/O
        objects, including:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
            <code class="computeroutput">boost::asio::ip::tcp::socket</code>
          </li>
<li class="listitem">
            <code class="computeroutput">boost::asio::ip::tcp::acceptor</code>
          </li>
<li class="listitem">
            <code class="computeroutput">boost::asio::ip::udp::socket</code>
          </li>
<li class="listitem">
            <a class="link" href="deadline_timer.html" title="deadline_timer"><code class="computeroutput">deadline_timer</code></a>.
          </li>
</ul></div>
<p>
        The <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a>
        class also includes facilities intended for developers of custom asynchronous
        services.
      </p>
<h5>
<a name="boost_asio.reference.io_service.h4"></a>
        <span class="phrase"><a name="boost_asio.reference.io_service.thread_safety"></a></span><a class="link" href="io_service.html#boost_asio.reference.io_service.thread_safety">Thread
        Safety</a>
      </h5>
<p>
        <span class="emphasis"><em>Distinct</em></span> <span class="emphasis"><em>objects:</em></span> Safe.
      </p>
<p>
        <span class="emphasis"><em>Shared</em></span> <span class="emphasis"><em>objects:</em></span> Safe, with the
        specific exceptions of the <code class="computeroutput">restart()</code> and <code class="computeroutput">notify_fork()</code>
        functions. Calling <code class="computeroutput">restart()</code> while there are unfinished <code class="computeroutput">run()</code>,
        <code class="computeroutput">run_one()</code>, <code class="computeroutput">run_for()</code>, <code class="computeroutput">run_until()</code>,
        <code class="computeroutput">poll()</code> or <code class="computeroutput">poll_one()</code> calls results in undefined
        behaviour. The <code class="computeroutput">notify_fork()</code> function should not be called while
        any <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a>
        function, or any function on an I/O object that is associated with the <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a>,
        is being called in another thread.
      </p>
<h5>
<a name="boost_asio.reference.io_service.h5"></a>
        <span class="phrase"><a name="boost_asio.reference.io_service.synchronous_and_asynchronous_operations"></a></span><a class="link" href="io_service.html#boost_asio.reference.io_service.synchronous_and_asynchronous_operations">Synchronous
        and asynchronous operations</a>
      </h5>
<p>
        Synchronous operations on I/O objects implicitly run the <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a>
        object for an individual operation. The <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a>
        functions <code class="computeroutput">run()</code>, <code class="computeroutput">run_one()</code>, <code class="computeroutput">run_for()</code>,
        <code class="computeroutput">run_until()</code>, <code class="computeroutput">poll()</code> or <code class="computeroutput">poll_one()</code>
        must be called for the <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a>
        to perform asynchronous operations on behalf of a C++ program. Notification
        that an asynchronous operation has completed is delivered by invocation of
        the associated handler. Handlers are invoked only by a thread that is currently
        calling any overload of <code class="computeroutput">run()</code>, <code class="computeroutput">run_one()</code>, <code class="computeroutput">run_for()</code>,
        <code class="computeroutput">run_until()</code>, <code class="computeroutput">poll()</code> or <code class="computeroutput">poll_one()</code>
        for the <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a>.
      </p>
<h5>
<a name="boost_asio.reference.io_service.h6"></a>
        <span class="phrase"><a name="boost_asio.reference.io_service.effect_of_exceptions_thrown_from_handlers"></a></span><a class="link" href="io_service.html#boost_asio.reference.io_service.effect_of_exceptions_thrown_from_handlers">Effect
        of exceptions thrown from handlers</a>
      </h5>
<p>
        If an exception is thrown from a handler, the exception is allowed to propagate
        through the throwing thread's invocation of <code class="computeroutput">run()</code>, <code class="computeroutput">run_one()</code>,
        <code class="computeroutput">run_for()</code>, <code class="computeroutput">run_until()</code>, <code class="computeroutput">poll()</code> or
        <code class="computeroutput">poll_one()</code>. No other threads that are calling any of these functions
        are affected. It is then the responsibility of the application to catch the
        exception.
      </p>
<p>
        After the exception has been caught, the <code class="computeroutput">run()</code>, <code class="computeroutput">run_one()</code>,
        <code class="computeroutput">run_for()</code>, <code class="computeroutput">run_until()</code>, <code class="computeroutput">poll()</code> or
        <code class="computeroutput">poll_one()</code> call may be restarted <span class="emphasis"><em>without</em></span>
        the need for an intervening call to <code class="computeroutput">restart()</code>. This allows the
        thread to rejoin the <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a>
        object's thread pool without impacting any other threads in the pool.
      </p>
<p>
        For example:
      </p>
<pre class="programlisting">boost::asio::io_context io_context;
...
for (;;)
{
  try
  {
    io_context.run();
    break; // run() exited normally
  }
  catch (my_exception&amp; e)
  {
    // Deal with exception as appropriate.
  }
}
</pre>
<h5>
<a name="boost_asio.reference.io_service.h7"></a>
        <span class="phrase"><a name="boost_asio.reference.io_service.submitting_arbitrary_tasks_to_the_io_context"></a></span><a class="link" href="io_service.html#boost_asio.reference.io_service.submitting_arbitrary_tasks_to_the_io_context">Submitting
        arbitrary tasks to the io_context</a>
      </h5>
<p>
        To submit functions to the <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a>,
        use the <a class="link" href="dispatch.html" title="dispatch"><code class="computeroutput">dispatch</code></a>
        , <a class="link" href="post.html" title="post"><code class="computeroutput">post</code></a> or
        <a class="link" href="defer.html" title="defer"><code class="computeroutput">defer</code></a> free
        functions.
      </p>
<p>
        For example:
      </p>
<pre class="programlisting">void my_task()
{
  ...
}

...

boost::asio::io_context io_context;

// Submit a function to the io_context.
boost::asio::post(io_context, my_task);

// Submit a lambda object to the io_context.
boost::asio::post(io_context,
    []()
    {
      ...
    });

// Run the io_context until it runs out of work.
io_context.run();
</pre>
<h5>
<a name="boost_asio.reference.io_service.h8"></a>
        <span class="phrase"><a name="boost_asio.reference.io_service.stopping_the_io_context_from_running_out_of_work"></a></span><a class="link" href="io_service.html#boost_asio.reference.io_service.stopping_the_io_context_from_running_out_of_work">Stopping
        the io_context from running out of work</a>
      </h5>
<p>
        Some applications may need to prevent an <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a>
        object's <code class="computeroutput">run()</code> call from returning when there is no more work
        to do. For example, the <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a>
        may be being run in a background thread that is launched prior to the application's
        asynchronous operations. The <code class="computeroutput">run()</code> call may be kept running
        by creating an executor that tracks work against the <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a>:
      </p>
<pre class="programlisting">boost::asio::io_context io_context;
auto work = boost::asio::require(io_context.get_executor(),
    boost::asio::execution::outstanding_work.tracked);
...
</pre>
<p>
        If using C++03, which lacks automatic variable type deduction, you may compute
        the return type of the require call:
      </p>
<pre class="programlisting">boost::asio::io_context io_context;
typename boost::asio::require_result&lt;
    boost::asio::io_context::executor_type,
    boost::asio::exeution::outstanding_work_t::tracked_t&gt;
  work = boost::asio::require(io_context.get_executor(),
    boost::asio::execution::outstanding_work.tracked);
...
</pre>
<p>
        or store the result in the type-erasing executor wrapper, <a class="link" href="any_io_executor.html" title="any_io_executor"><code class="computeroutput">any_io_executor</code></a>:
      </p>
<pre class="programlisting">boost::asio::io_context io_context;
boost::asio::any_io_executor work
  = boost::asio::require(io_context.get_executor(),
      boost::asio::execution::outstanding_work.tracked);
...
</pre>
<p>
        To effect a shutdown, the application will then need to call the <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a>
        object's <code class="computeroutput">stop()</code> member function. This will cause the <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a>
        <code class="computeroutput">run()</code> call to return as soon as possible, abandoning unfinished
        operations and without permitting ready handlers to be dispatched.
      </p>
<p>
        Alternatively, if the application requires that all operations and handlers
        be allowed to finish normally, store the work-tracking executor in an <a class="link" href="any_io_executor.html" title="any_io_executor"><code class="computeroutput">any_io_executor</code></a>
        object, so that it may be explicitly reset.
      </p>
<pre class="programlisting">boost::asio::io_context io_context;
boost::asio::any_io_executor work
  = boost::asio::require(io_context.get_executor(),
      boost::asio::execution::outstanding_work.tracked);
...
work = boost::asio::any_io_executor(); // Allow run() to exit.
</pre>
<h5>
<a name="boost_asio.reference.io_service.h9"></a>
        <span class="phrase"><a name="boost_asio.reference.io_service.requirements"></a></span><a class="link" href="io_service.html#boost_asio.reference.io_service.requirements">Requirements</a>
      </h5>
<p>
        <span class="emphasis"><em>Header: </em></span><code class="literal">boost/asio/io_service.hpp</code>
      </p>
<p>
        <span class="emphasis"><em>Convenience header: </em></span><code class="literal">boost/asio.hpp</code>
      </p>
</div>
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<td align="right"><div class="copyright-footer">Copyright © 2003-2021 Christopher
      M. Kohlhoff<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div></td>
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